Rod and cutting tool

ABSTRACT

A rod, a cutting tool and a method for manufacturing a cutting tool are disclosed. In an embodiment, the rod may include a cemented carbide member containing WC and Co. The cemented carbide member may be elongated and include a first end portion and a second end portion in a longitudinal direction. The first end portion may have a Co content Co AC  smaller than a Co content Co BC  of the second end portion. The cemented carbide member may include a first portion on a side of the first end portion and a second portion on a side of the second end portion. The first portion may have a gradient S 1  representing a change in a Co content per milliliter. The second portion may have a gradient S 2  representing a change in a Co content per milliliter. The gradient S 1  may be greater than the gradient S 2 .

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national stage entry of International ApplicationNo. PCT/JP2016/052324 under 35 U.S.C. § § 365 and 371, filed on Jan. 27,2016, which claims priority to Japanese Patent Application No. JP2015-130004, which was filed on Jun. 29, 2015, Japanese PatentApplication No. JP 2015-189048, which was filed on Sep. 26, 2015, andJapanese Patent Application No. JP 2015-229785, which was filed on Nov.25, 2015. The disclosures of each of the foregoing documents areincorporated herein by reference in their entirety and for all purposes.

FIELD

The disclosure relates to a rod, and an elongated cutting tool such as adrill or an end mill.

BACKGROUND

Elongated rods are used as structural members. A rod is used in, forexample, a cutting tool such as a drill or an end mill, which includesan elongated cylindrical rod called a blank on which cutting edges areformed. A drill for boring holes may be a solid drill, which includes arod having flutes extending from the tip cutting edges. The solid drillis used, for example, for boring holes on a substrate onto whichelectronic components are to be mounted.

For example, Patent Literature 1 describes a drill blank that hascompositions varying either radially or longitudinally.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Unexamined Patent Application PublicationNo. 2012-526664

SUMMARY

According to the disclosure, a rod includes cemented carbide membercontaining WC and Co. The rod is elongated and includes a first endportion and a second end portion in a longitudinal direction. The firstend portion has a Co content Co_(AC) and the second end portion has a Cocontent Co_(BC). The Co content Co_(AC) is smaller than the Co contentCo_(BC). The rod further includes a first portion on a side of the firstend portion and a second portion on a side of the second end andportion. The first portion has a gradient S₁ representing a change in aCo content. The second portion has a gradient S₂ representing a changein a Co content. The gradient S₁ is greater than the gradient S₂.

According to the disclosure, a cutting tool includes a cemented carbidemember containing WC and Co. The cemented carbide member is elongatedand includes a first end portion and a second end portion in alongitudinal direction. The cemented carbide member further includescutting edges at least on a side of the first end portion and a shankportion on a side of the second end portion. The first end portion has aCo content Co_(AC) smaller than a Co content Co_(BC) of the second endportion. The cemented carbide member further includes a first portion ona side of the first end portion and a second portion on a side of thesecond end portion. The first portion has a gradient S₁ representing achange in a Co content per milliliter. The second portion has a gradientS₂ representing a change in a Co content per milliliter. The gradient S₁is greater than the gradient S₂.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a side view of a cutting tool blank as an example of a rodaccording to the disclosure, FIG. 1B is a graph showing the distributionof the Co content in the cutting tool blank in FIG. 1A.

FIG. 2A is a side view of a cutting tool blank as another example of therod according to the disclosure, and FIG. 2B is a graph showing thedistribution of the Co content in the cutting tool blank in FIG. 2A.

FIG. 3 is a side view of a cutting tool blank as still another exampleof the rod according to the disclosure.

FIG. 4 is a schematic diagram of a mold used in a method for molding thecutting tool blank shown in FIG. 1A.

FIG. 5 is a side view of an example drill obtained by joining thecutting tool blank shown in FIG. 1A to a shank and forming cutting edgesin the blank.

DETAILED DESCRIPTION

A cutting tool blank as one example of a rod according to the disclosurewill be described with reference to FIGS. 1A to 2B. FIGS. 1A and 2A areside views of the cutting tool blank as examples of the rod according tothe disclosure. FIGS. 1B and 2B are graphs each showing the distributionof the Co content in the cutting tool blank. In FIGS. 1A and 1B, thedotted line indicates a drill that is formed by machining the cuttingtool blank to have a first end (hereafter, part A) with cutting edgesand a second end (hereafter, part B) connected to a shank.

A cutting tool blank (hereafter simply, the blank) 2 used for a drill 1in the present embodiment includes a cemented carbide member. Thecemented carbide member contains WC and Co. In FIG. 1A, the cementedcarbide member is included in a blank 2. The blank 2 in FIG. 1A includesa body 10 and a protrusion 15. The blank 2 may have a coating layer (notshown) on its surface.

The blank 2, which is elongated and cylindrical, includes part Aadjacent to one end in a longitudinal direction where cutting edges areformed, and part B adjacent to the other end in the longitudinaldirection to be joined to the shank 3. The blank 2 may also contain, aswell as WC and Co, carbides of metals in groups 4, 5, and 6 in theperiodic table excluding W. The carbides of metals in groups 4, 5, and 6in the periodic table may be Cr₃C₂, VC, TiC, TaC, NbC, and ZrC. Inparticular, the blank 2 including the cemented carbide member containingCr₃C₂ has high corrosion resistance. For the cemented carbide membercontaining Cr₃C₂ and VC, the cemented carbide with a uniform particlesize can be prepared in a stable manner by preventing abnormal growth ofWC particles. The blank 2 including the cemented carbide member having amean particle diameter less than 1.0 μm has high hardness and toughness.

In the present embodiment, the Co content Co_(AC) in part A of the blank2 is smaller than the Co content Co_(BC) in part B. This allows part Awith the cutting edges to have higher wear resistance, and enables aportion adjacent to part B, which is easily fractured in a cutting toolsuch as a drill or an end mill, to have higher fracture resistance. Inthe present embodiment, the blank 2 has a second portion 12 adjacent topart B and a first portion 11 adjacent to part A. The second portion 12has a gradient S₂ representing changes in its Co content, and the firstportion 11 has a gradient S₁ representing changes in its Co content. Thegradient S₁ is greater than the gradient S₂. This allows a wide-rangearea adjacent to part B to have higher toughness, without reducing thehigh wear resistance in part A. The blank 2 thus has higher fractureresistance.

In the present embodiment, part A and part B refer to the ends of theblank 2, and these parts are specifically to be at positions where thecomposition of the blank 2 can be analyzed using an electron probemicroanalyzer (EPMA). As shown in FIGS. 1B and 2B, the analysis usingthe EPMA in the ends of the blank 2 can inaccurately measure thecomposition when the measurement field partly deviates from the blank 2because of the spot size. Thus, Part A and part B are to be at positionswhere the measurement can be performed.

The Co content Co_(AC) may range from 0 to 10.0 percent by mass, and theCo content Co_(BC) may range from 2.0 to 16.0 percent by mass. Underthese conditions, the wear resistance and the fracture resistance of theblank 2 can be maintained high. Although more desirable ranges ofCo_(AC) and Co_(BC) depend on the machining conditions, the Co contentCo_(AC) may range from 0.2 to 7 percent by mass, and the Co contentCo_(BC) may range from 2 to 12 percent by mass. For example, in a drillfor processing a printed circuit board, the Co content Co_(AC) may rangefrom 1.0 to 4.9 percent by mass, and the Co content Co_(BC) may rangefrom 5.0 to 10.0 percent by mass. The conventional uniform compositioncannot easily allow densification of cemented carbide having a Cocontent of less than 5 percent by mass. More specifically, after fired,the blank 2 has a Co aggregation depending on the particle diameter andthe degree of aggregation of the Co material powder. The Co aggregationcauses ununiform Co distribution. In the present embodiment, however,the capillary action of Co causes Co diffusing, and thus a Coaggregation cannot easily occur. This allows a uniform Co distribution.Thus, a cemented carbide member adjacent to part A with a small Cocontent can be densified.

The ratio Co_(AC)/Co_(BC) of the Co content Co_(AC) to the Co contentCo_(BC) ranges from 0.2 to 0.7. The ratio in this range improves thehardness in part A, and increases the fracture resistance of the blank2. The ratio Co_(AC)/Co_(BC) can be determined by measuring thecomposition in each portion across the longitudinal section of the blank2 through the EPMA analysis. The longitudinal section is obtained bysplitting the blank 2 in half. The composition analysis of part A andpart B is performed along the central axis of the longitudinal section.

The gradients S₁ and S₂ represent the rate of change in the Co contentin the longitudinal direction. To determine the change in thecomposition of the blank 2 in the longitudinal direction, the Co contentdistribution in the blank 2 in the longitudinal direction is measuredthrough an EPMA analysis, and the first portion 11 and the secondportion 12 are identified. The gradient S₁ and the gradient S₂ arecalculated from the inclinations obtained by approximating thedistribution in each portion using the method of least squares. Downwardinclinations from part A to part B are defined as an increase in the Cocontent, whereas upward inclinations from part A to part B are definedas a decrease in the Co content.

When the gradient S₁ ranges from 0.2 to 1.0 percent by mass permilliliter, and the gradient S₂ ranges from 0 to 0.2 percent by mass permilliliter, the blank 2 may have an increased hardness in part A, aswell as an increased fracture resistance. The gradient S₁ may not beconstant within the first portion 11. In particular, as the gradientwithin the first portion 11 increases its inclination toward part A, thewear resistance in part A and the fracture resistance of the blank 2increase.

The blank 2 may have a diamond-coating layer (not shown) on its surface.The content Co at the surface of the first portion 11, which can preventthe growth of diamond crystals, is small, and thus the diamond-coatinglayer on the first portion 11 has higher crystallinity. Thediamond-coating layer thus has improved hardness and adhesion.

Additionally, the blank 2 may have a third portion 13 between the secondportion 12 and the first portion 11. The third portion 13 may have agradient S₃ greater than the gradient for the first portion 11. In thiscase, the gradient S₁ for the first portion 11 and the gradient S₂ forthe second portion 12 are easy to control. The control enables a portionadjacent to part B, which is easily fractured, to have still higherfracture resistance. The gradient S₃ of 2 to 50 percent by mass permilliliter increases the wear resistance of a portion adjacent to part Aand the fracture resistance of a portion adjacent to part B.

Additionally, the blank 2 may have a fourth portion 14 near part A thanthe first portion 11 as shown in FIGS. 2A and 2B. The fourth portion 14may have a gradient S₄ smaller than the gradient S₁. In this case, awear-resistant area adjacent to part A may be larger. For a gradient S₄of 0 to 0.5 percent by mass per milliliter and the Co content in thefourth portion 14 of 0 to 0.6 percent by mass, the diamond-coating layeron the surface of the blank 2 has still higher crystallinity on the partcorresponding to the fourth portion 14. The diamond-coating layer thushas improved hardness and adhesion in this area. The boundary betweenthe first portion 11 and the fourth portion 14 has an inflection pointin the Co content distribution.

The longitudinal length of the first portion 11 is L₁, the longitudinallength of the second portion 12 is L₂, the longitudinal length of thethird portion 13 is L₃, and the longitudinal length of the fourthportion 14 is L₄. In the ratio L₁/L₂ of 0.2 to 5.0, the hardness in partA is improved, and the fracture resistance of the blank 2 is increased.For the drill 1 used as a micro drill for processing printed circuitboards, the ratio L₁/L₂ may range from 0.2 to 5.0, the Co contentCo_(AC) may range from 0.3 to 8.0 percent by mass, and the Co contentCo_(BC) may range from 2.5 to 15.0 percent by mass.

In the ratio L₃/L₂ of 0.01 to 0.1, the Co content in the second portion12 and the Co content in the first portion 11 can be adjusted easily. Inthe ratio L₄/L₂ of 0 to 0.05, the cemented carbide member in part A isdensified easily in a more stable manner. When the ratio L₄/L₂ isgreater than 0.05 and the fourth portion 14 is partially not densified,at least a part in the fourth portion 14 may be ground away in formingthe drill 1.

The corners in part A of the longitudinal section obtained by splittingthe blank 2 in half correspond to the outer periphery in part A. Theblank having the Co content Co_(AO) in the outer periphery in part Asmaller than the Co content Co_(AC) of the center of part A may have anincreased wear resistance on its outer periphery, which can most easilywear in the cutting edges of a rotary tool such as a drill or an endmill.

The Co content in the outer periphery of part A is Co_(AO). The Cocontent Co_(AO) may range from 0.1 to 6.5 percent by mass, and the ratioCo_(AO)/Co_(AC) of the Co content Co_(AO) to the Co content Co_(AC) mayrange from 0.1 to 0.9. Under these conditions, the wear resistance ofthe cutting edges of a cutting tool is improved, and fractures in thecenter of the cutting tool tip are prevented.

When the diameter d_(A) of the blank 2 in part A and the diameter d_(B)in part B are both 2 mm or less, and the longitudinal length of theblank 2 is defined as L, the blank with the ratio L/d_(A) of the lengthL to d_(A) being 3 or more is difficult to form by extrusion. Morespecifically, changing the Co contents in part A and part B isdifficult, and forming the protrusion 15 is also difficult. However, theblank 2 having this shape can be formed by pressing. The manufacturingconditions such as the shape of the mold and the firing conditions areoptimized to reduce fractures in the mold and a compact and also controlthe composition and the shape of the fired blank to fall withinpredetermined limits.

In the ratio L/d_(A) of 3 or more, the Co contents Co_(AC) and Co_(BC)in the fired blank 2 can be easily adjusted to have a predeterminedproportion. At a smaller ratio L/d_(A), the Co diffusing during thefiring process can offset the difference between Co_(AC) and Co_(BC) inthe blank 2. The ratio L/d_(A) may desirably be 4 to 10.

The blank 2 with the diameters d_(A) and d_(B) of 0.2 to 2 mm, and thelength L of 3 to 20 mm is appropriate for a drill for processing printedcircuit boards. In particular, the diameter d_(A) may range from 0.3 to1.7 mm. In other applications, the diameter d_(A) may be greater than 2mm. In that case, the diameter d_(A) may range from 0.2 to 20 mm, andthe length L may be 3 to 50 mm.

In the present embodiment, the ratio d_(A)/d_(B) may range from 1.02 to1.20 as shown in FIG. 3. In this case, part A and part B can be easilydistinguished from each other based on the dimensional differencebetween part A and part B, which have different Co contents. The cuttingedges of the cutting tool can thus be formed in part A in a reliablemanner. The cutting tool can be obtained at a lower grinding costbecause the ratio d_(A)/d_(B) is 1.20 or less, and thus the machiningcost can be reduced. In some embodiments, the ratio d_(A)/d_(B) mayrange from 1.03 to 1.10.

In FIG. 3, an area a includes part A and has the ratio of its diameterto the diameter of part A being 0.95 or more, and an area b includespart B and has the ratio of its diameter to the diameter of part A beingless than 0.95. Under the conditions, the ratio L_(A)/(L_(A)+L_(B)) mayrange from 0.3 to 0.6, where L_(A) is the longitudinal length of thearea a, and L_(B) is the longitudinal length of the area b. In thisrange, the cutting edges of the drill 1 can maintain high wearresistance after being ground again, and the flutes can have higherfracture resistance. The ratio L_(A)/(L_(A)+L_(B)) may range from 0.3 to0.5.

The diameter across the area a decreases continuously from the diameterd_(A) of part A toward the diameter d_(B) of part B, which is the otherend. The diameter decreasing continuously refers to the diameterchanging without steps indicating discontinuous changes. This preventsfractures in the blank 2.

The fired blank 2 may not be ground. However, the outer peripheralsurface of the fired blank 2 may undergo centerless grinding to increasethe accuracy of positioning in holding the blank 2 during the processfor joining the blank 2 to the shank 3.

In FIGS. 1A to 2B, the protrusion 15 is formed at a positionlongitudinally outward from the end of the blank 2 adjacent to part A.The protrusion 15 has a smaller diameter than the blank 2. Theprotrusion 15 protrudes from a first end face 18 of the body 10. Thefirst end face 18 includes a protrusion area 16 having the protrusion15, and a circumferential area 17 along the circumference of theprotrusion area 16. In other words, the area of the protrusion 15 incontact with part A has a diameter d_(c) smaller than the diameter d_(A)of part A. The protrusion 15 allows part A and part B of the blank 2 tobe distinguished more easily.

The ratio d_(C)/d_(A) between the diameters d_(C) and d_(A) may rangefrom 0.5 to 0.9. In this range, fractures in the compact for the blank 2are prevented in the processes for manufacturing the blank 2. As shownin FIG. 3, the protrusion 15 has a height L_(C). The height L_(C) may be5 to 20% of the full length L of the blank 2.

The protrusion 15 can be formed easily. The tip of the drill 1 withcutting edges may be formed by the protrusion 15 to save the machiningcost.

The protrusion 15 is tapered. In particular, the protrusion 15 may havea round tip. The protrusion 15 is hemispherical in FIGS. 1A to 3. Thisprotrusion 15 is prevented from chipping and also from damaging otherblanks 2 when the blanks 2 randomly placed into a joining machine maycollide with one another. In the present embodiment, the bottom of theprotrusion 15 in contact with part A has a round surface in alongitudinal section. FIG. 4 is a schematic diagram of a mold used in amethod for molding the cutting tool blank according to the presentembodiment. The bottom of each protrusion 15 in contact with part A hasthe round surface in a longitudinal section. This prevents a lower punch23 from receiving a concentrated load and chipping during molding of acompact 35.

The protrusion 15 according to a first embodiment has the Co contentCo_(CC) smaller than the Co content Co_(AC) in part A. In this case, thecutting edges of the drill 1 formed from the protrusion 15 and part Ahave high wear resistance. Part B, which has a high Co content, has hightoughness. The flutes of the drill 1 formed in a portion adjacent topart B has high fracture resistance. Thus, the cutting tool in thepresent embodiment using the blank 2 has high wear resistance in itscutting edges, and also has high fracture resistance. In this structure,the cutting edges 5 formed from the protrusion 15 or part A only alsohave high wear resistance. The drill 1 including the cutting edges 5with tips formed from the protrusion 15 has high straightness in boringholes, and thus has higher accuracy in boring holes.

For the protrusion 15 according to the first embodiment, the Co contentin the center of part A is Co_(AC), the Co content in the center of partB is Co_(BC), and the Co content in the tip of the protrusion 15 isCo_(CC). The Co content Co_(AC) may range from 0.2 to 7 percent by mass,the Co content Co_(BC) may range from 2 to 12 percent by mass, the Cocontent Co_(CC) may range from 0.1 to 6 percent by mass, the ratioCo_(AC)/Co_(BC) of the Co content Co_(AC) to the Co content Co_(BC) mayrange from 0.1 to 0.6, and the ratio Co_(CC)/Co_(AC) of the Co contentCo_(CC) to the Co content Co_(AC) may range from 0.1 to 0.8. Withinthese ranges, the drill 1 has high fracture resistance and includes thecutting edges with high wear resistance. Further, the cutting edges 5 atleast with their tips formed from the protrusion 15 increase theaccuracy in boring holes.

The protrusion 15 according to a second embodiment has the Co contentCo_(CC) greater than the Co content Co_(AC) in part A. In this case, theprotrusion 15 has a high Co content and low hardness, and thus theprotrusion 15 may be easily ground away in forming a drill using theblank 2.

In the present embodiment, the Co content in the center of part A isgreater than the Co content in the outer periphery of part A. Thus, arotary tool such as an end mill (not shown) including the blank 2 has acutting tool tip having the cemented carbide hardness that is lower inthe central area at and near the center of rotation. For the cuttingtool tip with its central area containing a low-hardness material, thecutting speed is nearly zero at or near the center of rotation of thecutting tool. This prevents fractures in the center of the end mill tipwhen the cutting tool rubs against a workpiece.

For the protrusion 15 according to the second embodiment, the Co contentCo_(AC) may range from 0.2 to 7 percent by mass, the Co content Co_(BC)may range from 3 to 12 percent by mass, the Co content Co_(CC) may rangefrom 2 to 12 percent by mass, the ratio Co_(AC)/Co_(BC) of the Cocontent Co_(AC) to the Co content Co_(BC) may range from 0.1 to 0.6, andthe ratio Co_(CC)/Co_(AC) of the Co content Co_(CC) to the Co contentCo_(AC) may range from 1.2 to 3. Within these ranges, the end mill hashigh fracture resistance and includes the cutting edges with high wearresistance. Further, the protrusion 15 may be easily ground away whenthe end mill is machined.

The Co contents Co_(AC), Co_(AO), Co_(BC) and Co_(CC) can be determinedby measuring the composition in each portion in the longitudinaldirection of the blank 2 using the EPMA analysis. The longitudinalsection is obtained by splitting the blank 2 in half. To determine thechange in the composition of the blank 2 in the longitudinal direction,an electron microscope observation is performed along a side surface ofthe blank 2 while the measurement position is being shifted in astepwise manner. The composition in each portion is measured through theEPMA analysis to determine the change in the composition.

Although the present embodiment describes a drill as a cutting tool forboring holes in printed circuit boards, the disclosure may be directedto any tool having an elongated body. For example, the disclosure may bedirected to a metalworking drill, a medical drill, an end mill, and acutting tool for turning, such as an indexable insert for inner diametermachining. The rod such as the blank 2 may be used not only for acutting tool, but also as a wear-resistant member and a sliding member.For example, the rod may also be used as a punch. For applications otherthan cutting tools, the rod may also be processed into a predeterminedshape, and an area including part A may be placed in contact with thetarget material while part B is fixed.

Method for Manufacturing Blank

A method for manufacturing the cutting tool blank described above willnow be described. First, material powders such as WC powder are mixed toprepare cemented carbide for a blank and a cutting tool. In the presentembodiment, three material powders are mixed.

More specifically, the mixed material powders prepared include a firstmaterial powder containing WC powder for forming a protrusion, a secondmaterial powder containing WC powder for forming a portion adjacent topart A, and a third material powder containing WC powder and Co powderfor forming a portion adjacent to part B. The second material powder mayalso contain Co powder in addition to WC powder. However, the secondmaterial powder has a smaller Co content smaller than the third materialpowder. The mass ratio of the Co powder content in the second materialpowder to the Co powder content in the third material powder is 0 to0.5, and specifically 0 to 0.3. In addition to WC powder and Co powder,the first material powder, the second material powder, and the thirdmaterial powder may also contain any additive of the powders ofcarbides, nitrides, and carbonitrides of the metals in groups 4, 5, and6 in the periodic table excluding WC.

When no protrusion is to be formed, the first material powder iseliminated. When a protrusion having the Co content Co_(CC) smaller thanthe Co content Co_(AC) in part A is to be formed, the first basematerial powder may be replaced by the second base material powder.

For forming a protrusion having the Co content Co_(CC) greater than theCo content Co_(AC) in part A, the first material powder contains Copowder in addition to WC powder, and the Co powder content in the firstmaterial powder is greater than the Co powder content in the secondmaterial powder.

For forming a protrusion having the Co content Co_(CC) greater than theCo content Co_(AC) in part A, the mixture proportion of the WC powder inthe first material powder may range from 65 to 95 percent by mass, themixture proportion of the Co powder may range from 3 to 30 percent bymass, and the mixture proportion of the additives may range from 0 to 5percent by mass in total. The mixture proportion of the WC powder in thesecond material powder may range from 90 to 100 percent by mass, themixture proportion of the Co powder may range from 0 to 8 percent bymass, and the mixture proportion of the additives may range from 0 to 5percent by mass in total. The mixture proportion of the WC powder in thethird material powder may range from 65 to 95 percent by mass, themixture proportion of the Co powder may range from 4 to 30 percent bymass, and the mixture proportion of the additives may range from 0 to 10percent by mass in total.

A binder and a solvent are added to the material powders to obtainslurry. This slurry is granulated, and the resultant granules are usedas a powder to be used for molding. For ease of explanation, aprotrusion having the Co content Co_(CC) greater than the Co contentCo_(AC) in part A is formed in the molding process described below.

In the molding process, a press mold (hereafter simply, the mold) 20 isprepared, and the granules are placed into cavities 22 in a die 21 ofthe mold 20 as shown in FIG. 4. The granules placed in each cavity 22 inthe die 21 are pressurized by lowering an upper punch 24 to form acompact. In the present embodiment, the bottoms of the cavities 22 aredefined by the upper surfaces of lower punches 23, which serve as thepress surfaces. Each upper surface has a hollowed space 25 for formingthe protrusion 15. The diameter D_(C) of the compact 35 at the positionof the contact between a raw protrusion 32 and a compact lower part 31corresponds to the diameter of the opening for the raw protrusion 32.The ratio D_(C)/D_(A) of the diameter D_(C) to the upper surfacediameter of the lower punch D_(A) may range from 0.5 to 0.9. Thisreduces stress concentration during the pressurization, and preventsfractures in the lower punch 23.

The molding method includes placing the first material powder 30 intothe hollowed space 25 included in the cavity 22; placing the secondmaterial powder 33 into the cavity 22; placing the third material powder37 into the cavity 22; lowering the upper punch 24 from above topressurize the first material powder 30, the second material powder 33,and the third material powder 37 placed in the cavity 22 in the die 21;and releasing the layered compact 35 from the mold 20.

The compact 35 is elongated and cylindrical, and has the Co content inpart A smaller than the Co content in part B. Thus, the blank 2 has apredetermined Co content distribution. Adjusting the Co content in partC allows the Co content in part A of the fired blank 2 at the center andalong the outer periphery to fall within predetermined limits.

Other molding methods may be used. One such method includes placing thefirst material powder 30 and the second material powder 33, and thenfirst pressurizing these material powders. This is then followed byplacing the third material powder 37 on the upper surface of thecompact, and then repressurizing the compact. Another method includesplacing the first material powder 30, the second material powder 33, andthe third material powder 37 into the hollowed space 25 in the cavity22, and then lowering the upper punch 24 from above to pressurize thefirst material powder 30, the second material powder 33, and the thirdmaterial powder 37 placed in the cavity 22 in the die 21 together.

The round bottom of the hollowed space 25 can prevent the raw protrusion32 of the compact 35 from chipping, and reduce variations in the Cocontent in the protrusion 15 of the fired blank 2 to prevent locallypoor sintering of the compact.

To obtain a sintered body having a diameter of 2 mm or less in thepresent embodiment, an additional load is applied to the upper punch 24to lower the upper punch 24 by 0.1 to 2 mm, or 0.1 to 20% of the lengthof the compact, from the position of the upper punch 24 held during thepressurization, and also the load on the lower punch 23 is reduced.Under these molding conditions, the unevenness of pressure in thecompact 35 can be reduced, the lower punch 23 can be prevented frombeing fractured when the compact 35 is released, and the blank 2obtained by firing the compact 35 can have a predetermined shape.

More specifically, when the compact 35 for forming a sintered body witha diameter of greater than 2 mm is to be formed by pressing, thegranules, or powder, are homogeneously placed into the mold 20. With theconventional method for forming the compact 35 to obtain a sintered bodywith a diameter of 2 mm or less by pressing, the granules, or powder,can be placed inhomogeneously into the mold. In the present embodiment,the molding conditions are controlled to form the compact 35, and thento form the blank 2 having a predetermined shape.

As shown in FIG. 4, the diameter D_(A) of the compact 35 adjacent to thelower punch 23 may be smaller than the diameter D_(B) adjacent to theupper punch 24. For the compact resulting from the molding describedabove, the ratio D_(A)/D_(B) in the present embodiment may range from0.80 to 0.99. The ratio d_(A)/d_(B) in this range can be controlled tobe within intended limits. More specifically, the ratio d_(A)/d_(B) canbe controlled to be within intended limits based on the difference infiring shrinkage between part A and part B during firing. The ratioH_(A)/(H_(A)+H_(B)) may range from 0.2 to 0.7, where H_(A) is the heightof the second material powder 33 in the compact 35, and H_(B) is theheight of the third material powder 37. The compact may include anothermaterial powder such as a fourth material powder, for example, betweenthe second material powder 33 and the third material powder 37. Thefourth material powder may have a Co powder content falling between theCo powder contents in the second material powder 33 and the thirdmaterial powder 37.

To increase the manufacturing efficiency and to prevent the upper punchfrom lowering in an inclined direction, the mold includes multiple setsof the upper punch, the recess, and the lower punch, which allowmultiple compacts to be molded at a time. For example, the mold mayinclude 4 to 144 sets of the upper punch, the recess, and the lowerpunch. As viewed from the side, the mold may also have the upper punchesand the lower punches that each have the same diameter and are straight.In some embodiments, a portion adjacent to the lower punch, which ismore subject to pressure than a portion adjacent to the upper punch,shrinks less when fired. This difference in shrinkage may be reflectedin using the mold 20, or specifically the powder filling portion(recess) 22 in the die 21 is filled with granules, and the granules arepressed between the upper punch 24 and the lower punch 23 bypressurization. With the dimensional ratio d_(A)/d_(B) between theportion adjacent to the upper punch and the portion adjacent to thelower punch falling within predetermined limits, the diameter D_(A)adjacent to the lower punch 23 may be smaller than the diameter D_(B)adjacent to the upper punch 24 in the mold 20 as shown in FIG. 4. Underthese conditions, the lower punch 23 is prevented from receiving aconcentrated load on its periphery to prevent fractures in the lowerpunch 23.

The compact is then released from the mold and undergoes sinter hotisostatic pressing (sinter-HIP) firing to form the blank 2. The firingprocess in the present embodiment uses a temperature rise rate of 4 to20° C./min, a firing temperature of 1350 to 1580° C., and a firing timeperiod of 15 to 45 minutes. Under the conditions, the Co contents inpart A and part B can be easily adjusted. The differing degrees ofsintering between the second material powder 33 and the third materialpowder 37 cause part A and part B to have different shrinkages duringthe firing process. As a result, the compact is deformed, and theshrinkage of part B exceeds the shrinkage of part A. More specifically,the firing causes Co in part B to partly diffuse to part A, causing partB to shrink more than part A. In this manner, the sintered body can becontrolled to have an intended shape. The protrusion 15 is located tocause Co to diffuse less than in part A. The Co content Co_(C) in theprotrusion 15 is thus smaller than the Co content Co_(A).

Additionally, the differing degrees of sintering between the secondmaterial powder 33 and the third material powder 37 cause part A andpart B to have different shrinkages during the firing process. As aresult, the compact is deformed, and the shrinkage of part B exceeds theshrinkage of part A. More specifically, the firing causes Co in part Bto partly diffuse to part A, causing part B to shrink more than part A.In the sintered body, the diameter of part B thus tends to be smallerthan the diameter of part A.

At the temperature rising rate smaller than 4° C./min, Co can diffuseexcessively during the firing process. In this case, the Coconcentration difference in the sintered blank 2 tends to be small, andthe gradient S₁ for the first portion 11 becomes smaller than thegradient S₂ for the second portion 12, or the Co contents Co_(AC) andCo_(BC) become equal to each other. At the temperature rise rate higherthan 20° C./min, the gradient S₁ for the first portion 11 becomes equalto or smaller than the gradient S₂ for the second portion 12. Part A canbe insufficiently densified. Under the reduced pressure smaller than 50Pa at the firing temperature, Co can diffuse excessively during thefiring process, and the Co concentration in the sintered body becomesuniform. In this case, the gradient S₁ for the first portion 11 becomesequal to or smaller than the gradient S₂ for the second portion 12 orthe Co contents Co_(AC) and Co_(BC) become equal to each other. Underthe reduced pressure higher than 200 Pa, the gradient S₁ for the firstportion 11 becomes equal to or smaller than the gradient S₂ for thesecond portion 12, and part A may be insufficiently densified. When thedifference between the sinter-HIP processing temperature and thesintering temperature is 5° C. or less, the gradient S₁ for the firstportion 11 is equal to or smaller than the gradient S₂ of the secondportion 12 or the Co contents Co_(AC) and Co_(BC) become equal to eachother.

With the method for manufacturing the blank 2 according to the presentembodiment, the blank 2 is molded by pressing, and thus the blank 2 iseasily formed through a fewer molding processes. Further, the blank 2can have accurate dimensions with small dimensional changes between thecompact for the blank 2 and the fired blank 2. Thus, the blank 2 isshaped to have small machining allowance against the shape of the drill1. The blank 2 formed by pressing can have a smaller amount of binderadded during the molding than a blank 2 to be formed by extrusion. Theresultant blank 2 is a highly reliable component with less defects suchas voids and carbon residues in the sintered body (blank 2). In theprocess for molding the blank 2, the unevenness of density in thecompact can be regulated to allow stable molding with less chipping orother defects.

For the blank 2 having a diameter d_(A) of 2 mm or less, the compactformed by pressing can involve density variations. Due to this, thecemented carbide can sinter faster in the ends of the blank 2 (parts Aand B) than in the middle portion C. For the compact with the diameterD_(B) greater than the diameter D_(A), the cemented carbide sintersfaster in part A than in part B. In the present embodiment, the state ofthe granules used in the molding is adjusted. Additionally, after thepressurization using the upper and lower punches, an additional load isapplied using the upper punch 24 to prevent the mold from beingfractured and to adjust the density of the compact in the two ends ofthe blank 2. This reduces the dimensional difference between part A andpart B of the fired blank 2 to reduce the machining allowance.

The molding process according to the disclosure is not limited to thepressing described above. Examples of other molding techniques includecold isostatic pressing, dry-bag isostatic pressing, and injectionmolding.

Method for Manufacturing Cutting Tool

A method for manufacturing a drill for processing printed circuit boardsusing the blanks 2 obtained through the above processes will now bedescribed. Tens or hundreds of blanks 2 are randomly placed into ajoining machine. In the joining machine, the blanks 2 are alignedlongitudinally. When the blanks 2 each have the protrusion 15, theprotrusion 11 is detected using image data or other data, and part A andpart B of the blank 2 are identified. Using the identified parts A andB, the blanks 2 can be automatically aligned to have their parts A and Barranged in a predetermined direction.

Each of the blanks aligned with one another is then automatically placedin contact with a predetermined portion of a neck 7, which is connectedto a separately prepared shank 3, and then undergoes joining using alaser. The joined blank 2 then undergoes the cutting edge formation. Inthis state, as shown in FIG. 5, the drill 1 includes part A adjacent tothe cutting edges 5, and part B adjacent to the shank 3 of the drill 1.

Cutting Tool

The blank 2 then undergoes the process for forming cutting edges tocomplete the cutting tool, such as the drill 1. The drill 1 in FIG. 5includes a body 8 including cutting edges 5 in part A, flutes 6extending from the cutting edges, and a neck 7. The cutting edges 5 andthe flutes 6 correspond to a processing part. The drill 1 also includesa shank 3 adjacent to the body 8. The cutting edges 5, which first comein contact with a workpiece material while rotating about the centralaxis, need to have high chipping resistance and wear resistance. Theflutes 6 can clear away chips, resulting from machining, rearward. Theneck 7 smoothly connects the processing diameter (the diameter of theflutes 6) of the drill 1 to the diameter of the shank 3. The shank 3 isused to fix the drill 1 to a processing machine.

The drill 1 obtained by the method described above includes theprocessing part including the cemented carbide cutting edges 5 and theflutes 6. In the present embodiment, the maximum diameter of theprocessing part may be 2 mm or less.

Additionally, the surface of the drill 1 may be covered with a coatinglayer (not shown) as appropriate. The coating layer may be TiN, TiCN,TiAlN, diamond, and diamondlike carbon formed by physical vapordeposition (PVD), and diamond formed by chemical vapor deposition (CVD).

The neck 7 and the shank 3 may be formed from an inexpensive materialsuch as steel, alloy steel, or stainless steel, and the blank 2 may bejoined to the tip of the neck 7. In the drill 1, the section from thecutting edges 5 to the shank 3 may be formed using the blank. In someembodiments, the drill 1 may eliminate the neck 7.

In the present embodiment, to measure the mean particle diameter of theWC particles in part A and part B, the field of view in which 10 or moreWC particles are observed is defined in part A or part B, and the meanparticle diameter of the WC particles is measured in the defined fieldof view. The mean particle diameter of the WC particles in the field ofview may also be calculated by converting the area of each observed WCparticle into a circle, and calculating the average of the diameters ofthe circles representing the WC particles.

The neck 7 and the shank 3 may be formed from an inexpensive materialsuch as steel, alloy steel, or stainless steel, and the blank 2 may bejoined to the tip of the neck 7. In the drill 1, the section from thecutting edges 5 to the shank 3 may be formed using the blank 2. In someembodiments, the drill 1 may eliminate the neck 7. Additionally, thecutting tool may not be the drill 1, and may be used for, for example, adevice with a rotation axis, such as an end mill or a reamer.

EXAMPLE 1

Two types of powder mixtures, which are first material powders andsecond material powders in Table 1, were prepared by mixing cobalt (Co)metal powder, chromium carbide (Cr₃C₂) powder, vanadium carbide (VC)powder, and the remainder that is tungsten carbide (WC) powder with amean particle diameter of 0.3 μm at the proportions shown in Table 1.Additives including a binder and a solvent were added to each powdermixture to obtain slurry, which was then granulated with a spray dryerto produce granules with a mean particle diameter of 70 μm.

The mold shown in FIG. 3 including the die having 144 recesses wasprepared. The first material powders shown in Table 1 were placed in themold, and then the second material powders shown in Table 1 were placedin the mold, and then the mold underwent pressing. This forms compactseach including the first material powder, and the second material powderstacked on the first powder. The compacts were released from the mold.The shape of each compact is defined using a diameter D_(A) of a portionadjacent to the lower punch, a diameter D_(B) of a portion adjacent tothe upper punch, a length H_(A) of a lower part of the compact, and alength H_(B) of an upper part of the compact as shown in Table 1.

The compacts were heated at temperature rising from 1000° C. at thetemperature rise rates shown in Table 2, and then fired for one hourunder the atmospheres and the firing temperatures shown in Table 2.Then, the temperatures were changed to sinter-HIP temperatures (HIP inthe table) shown in Table 2. The compacts then underwent sinter-HIPprocessing under a pressure of 5 MPa for 30 minutes.

The length of each resultant blank was measured by measuring thediameters of part A and part B of the blank. Table 2 shows the results(d_(A) and d_(B)). Each blank was longitudinally split in half. Thechanges in the Co content across the section from part A to part B werethen measured through the EPMA analysis to detect the second to fourthportions, the gradients, and the lengths. For part A of each blank, theCo content along the outer periphery was measured. Tables 2 and 3 showthe results.

After the outer periphery of each blank underwent centerless grinding,the blanks were randomly placed into a joining machine. In the joiningmachine, the protrusion of each blank was detected, and the blanks werealigned to have their parts A and parts B of the bodies arranged in thesame directions. The second end of the blank was placed in contact withand joined to a shank, and cutting edges were formed in a sectionincluding the first end of the blank to complete the drill.

The resultant drills were tested for drilling under the conditionsdescribed below. Table 3 shows the results.

Drilling Test Conditions

Workpiece material: FR4 material, 0.8 mm thick, three-layer stack

Drill shape: φ0.25 mm

Revolutions: 160 krpm

Feeding speed: 3.2 m/min

Evaluation items: the number of successfully bored pieces and the flankwear width (μm) of the tested drill

TABLE 1 First material powder Second material powder Compact size SampleCo added Added Co added Added D_(A) D_(B) D_(A)/ H_(A) H_(B) H_(A)/ No.(mass %) Additive (mass %) (mass %) Additive (mass %) (mm) (mm) D_(B)(mm) (mm) (H_(A) + H_(B)) I-1 — Cr₃C₂ 0.2 8.0 Cr₃C₂ 0.6 1.58 1.63 0.975.5 5.5 0.5 VC 0.1 VC 0.3 I-2 — Cr₃C₂ 0.3 8.0 Cr₃C₂ 0.5 1.58 1.63 0.972.5 8.5 0.2 VC 0.1 VC 0.3 I-3 — Cr₃C₂ 0.2 8.0 Cr₃C₂ 0.4 1.58 1.63 0.978.5 2.5 0.8 VC 0.1 VC 0.3 I-4 2.0 VC 0.2 8.0 Cr₃C₂ 0.2 2.35 2.35 1.005.5 5.5 0.5 VC 0.4 I-5 — — 8.0 Cr₃C₂ 0.6 1.28 1.35 0.95 5.5 5.5 0.5 I-6— Cr₃C₂ 0.2 8.0 Cr₃C₂ 0.6 1.58 1.63 0.97 5.5 5.5 0.5 VC 0.1 VC 0.3 I-7 —Cr₃C₂ 0.2 8.0 Cr₃C₂ 0.6 1.58 1.63 0.97 5.5 5.5 0.5 VC 0.1 VC 0.3 I-8 —Cr₃C₂ 0.2 8.0 Cr₃C₂ 0.6 1.58 1.63 0.97 5.5 5.5 0.5 VC 0.1 VC 0.3 I-9 —Cr₃C₂ 0.2 8.0 Cr₃C₂ 0.6 1.58 1.63 0.97 5.5 5.5 0.5 VC 0.1 VC 0.3 I-10 —Cr₃C₂ 0.2 8.0 Cr₃C₂ 0.6 1.58 1.63 0.97 5.5 5.5 0.5 VC 0.1 VC 0.3 I-11 —Cr₃C₂ 0.2 8.0 Cr₃C₂ 0.6 1.58 1.63 0.97 5.5 5.5 0.5 VC 0.1 VC 0.3 I-125.0 Cr₃C₂ 0.4 5.0 Cr₃C₂ 0.4 1.58 1.63 0.97 5.5 5.5 0.5 VC 0.3 VC 0.3I-13 2.0 Cr₃C₂ 0.2 2.0 Cr₃C₂ 0.2 1.58 1.63 0.97 5.5 5.5 0.5 VC 0.1 VC0.1 I-14 — Cr₃C₂ 0.2 8.0 Cr₃C₂ 0.6 1.58 1.63 0.97 5.5 5.5 0.5 VC 0.1 VC0.3 I-15 3.0 Cr₃C₂ 0.2 7.0 Cr₃C₂ 0.6 1.58 1.63 0.97 5.5 5.5 0.5 VC 0.1VC 0.3 I-16 3.0 Cr₃C₂ 0.2 7.0 Cr₃C₂ 0.6 1.58 1.63 0.97 5.5 5.5 0.5 VC0.1 VC 0.3 I-17 — Cr₃C₂ 0.2 8.0 Cr₃C₂ 0.6 1.58 1.63 0.97 5.5 5.5 0.5 VC0.1 VC 0.3 I-18 — Cr₃C₂ 0.2 8.0 Cr₃C₂ 0.6 1.58 1.63 0.97 5.5 5.5 0.5 VC0.1 VC 0.3 I-19 — Cr₃C₂ 0.2 8.0 Cr₃C₂ 0.6 1.58 1.63 0.97 5.5 5.5 0.5 VC0.1 VC 0.3

TABLE 2 Firing conditions Blank Temperature Reduced Firing HIPTemperature Diameter Sample rise rate pressure temperature temperaturedifference Length (mm) (mm) No. (° C./min) (Pa) (° C.) (° C.) (° C.) LL₄ L₁ L₃ L₂ d_(A) d_(B) L/d_(A) I-1 5.0 80 1380 1370 10 8.8 0.0 4.5 0.14.2 1.34 1.32 6.6 I-2 4.5 100 1370 1360 10 8.8 0.0 2.4 0.1 6.3 1.33 1.316.6 I-3 6.0 150 1390 1375 15 9.0 0.1 5.9 0.1 2.9 1.35 1.33 6.7 I-4 5.080 1400 1390 10 8.7 0.0 4.4 0.1 4.2 2.03 1.92 4.3 I-5 5.0 60 1380 137010 8.8 0.0 4.4 0.1 4.3 1.10 1.08 8.0 I-6 4.0 100 1380 1370 10 8.8 0.04.5 0.1 4.2 1.33 1.25 6.6 I-7 7.0 100 1380 1370 10 8.9 0.1 4.5 0.1 4.21.36 1.32 6.5 I-8 5.0 50 1380 1370 10 8.8 0.0 4.5 0.1 4.2 1.33 1.25 6.6I-9 5.0 200 1380 1370 10 8.8 0.1 4.5 0.1 4.2 1.36 1.32 6.5 I-10 5.0 1001380 1375 5 8.8 0.0 4.5 0.1 4.2 1.33 1.25 6.6 I-11 5.0 100 1380 1360 208.8 0.0 4.5 0.1 4.2 1.36 1.32 6.5 I-12 5.0 100 1380 1370 10 8.9 0.0 8.91.33 1.33 6.7 I-13 5.0 100 1380 1370 10 9.8 0.0 9.8 1.46 1.42 6.7 I-143.0 100 1380 1370 10 8.8 0.0 8.8 1.33 1.25 6.6 I-15 8.0 100 1380 1370 109.1 0.2 4.4 0.1 4.4 1.36 1.32 6.7 I-16 7.0 30 1380 1370 10 8.7 0.0 8.71.33 1.25 6.5 I-17 7.0 300 1380 1370 10 9.1 0.2 4.4 0.1 4.4 1.36 1.326.7 I-18 10.0 100 1380 1376 4 8.7 0.0 8.7 1.33 1.25 6.5 I-19 10.0 1001380 1355 25 9.0 0.1 4.4 0.1 4.4 1.36 1.32 6.6

TABLE 3 Blank Flank Co content wear Number of Sample (mass %) Co_(AC)/(mass %/mm) width processed No. Co_(AO) Co_(AC) Co_(BC) Co_(BC) S₄ S₁ S₃S₂ (μm) pieces I-1 1.5 1.8 5.0 0.36 — 0.42 12.0 0.024 120 5000 I-2 1.82.0 6.3 0.32 — 0.96 14.0 0.095 130 4600 I-3 0.0 0.0 4.0 0.00 0.00 0.476.0 0.207 180 4000 I-4 2.3 3.4 4.8 0.71 — 0.14 7.0 0.024 180 3800 I-52.4 3.5 4.7 0.74 — 0.11 6.0 0.023 200 3700 I-6 1.7 2.5 4.2 0.60 — 0.226.0 0.024 190 4300 I-7 0.0 0.0 7.0 0.00 0.00 1.00 22.0 0.071 160 4100I-8 1.8 2.6 4.2 0.62 — 0.20 6.0 0.024 190 4200 I-9 0.0 1.4 7.0 0.20 0.000.69 22.0 0.071 170 4300 I-10 2.1 2.6 4.0 0.65 — 0.20 4.0 0.024 170 4400I-11 0.0 1.5 7.0 0.21 — 0.73 22.0 0.071 160 4300 I-12 5.0 1.00 — 3502400 I-13 2.0 1.00 — — Initial fracture I-14 3.8 4.0 4.5 0.89 — 280 2400I-15 1.2 1.5 6.8 0.22 — 0.52 7.0 0.523 250 2300 I-16 3.8 4.0 4.5 0.89 —290 2100 I-17 1.1 1.2 6.8 0.18 — 0.56 6.2 0.568 260 2500 I-18 3.8 4.04.5 0.89 — 320 2600 I-19 1.2 1.4 6.6 0.21 — 0.41 15.0 0.432 260 2600

As shown in Tables 1 to 3, sample No. I-12 with Co_(AC) equal to Co_(BC)had a large flank wear width, and sample No. I-13 with Co_(AC) equal toCo_(BC) fractured at the first boring due to insufficient sintering.Sample Nos. I-14, I-16, and I-18 with no first and second portions had alarge flank wear width. Sample Nos. I-15, I-17, and I-19 with thegradient S₁ equal to or smaller than the gradient S₂ had low fractureresistance, and successfully processed a small number of pieces.

In contrast, sample Nos. I-1 to I-11 with Co_(AC) smaller than Co_(BC)and with the gradient S₁ of the first portion larger than the gradientS₂ of the second portion had a small flank wear width, and successfullyprocessed a large number of pieces.

In particular, sample Nos. I-1, I-2, I-6, and I-8 to I-11 with the ratioCo_(AC)/Co_(BC) ranging from 0.2 to 0.7 successfully processed a largenumber of pieces. Sample Nos. I-1, I-2, and I-6 to I-11 with thegradient S₁ ranging from 0.2 to 1.0 percent by mass per milliliter andwith the gradient S₂ ranging from 0 to 0.20 percent by mass permilliliter successfully processed a large number of pieces.

EXAMPLE 2

The material powders used in Example 1 were also used to form compactsshown in Table 4. The compacts were fired under the conditions shown inTable 5. The blanks were used to form drills. The resultant drills weretested for drilling under the conditions described below. Tables 5 and 6show the results.

Drilling Test Conditions

Workpiece material: FR4 material, one 24-layer stack, 3.2 mm thick

Drill shape: φ0.25 mm

Revolutions: 160 krpm

Feed speed: 3.2 m/min

Evaluation items: the number of successfully bored pieces and the flankwear width (μm) of the tested drill

TABLE 4 First material powder Second material powder Compact size SampleCo added Added Co added Added D_(A) D_(B) D_(A)/ H_(A) H_(B) H_(A)/ No.(mass %) Additive (mass %) (mass %) Additive (mass %) (mm) (mm) D_(B)(mm) (mm) (H_(A) + H_(B)) II-1 — Cr₃C₂ 0.2 5.0 Cr₃C₂ 0.5 1.58 1.63 0.975.5 5.5 0.5 VC 0.1 VC 0.2 II-2 — Cr₃C₂ 0.2 5.0 Cr₃C₂ 0.5 1.58 1.63 0.972.5 8.5 0.2 VC 0.1 VC 0.3 II-3 — Cr₃C₂ 0.2 5.0 Cr₃C₂ 0.4 1.58 1.63 0.978.5 2.5 0.8 VC 0.1 VC 0.3 II-4 2.0 Cr₃C₂ 0.2 5.0 Cr₃C₂ 0.4 1.58 1.630.97 5.5 5.5 0.5 VC 0.1 VC 0.3 II-5 5.0 Cr₃C₂ 0.2 5.0 Cr₃C₂ 0.2 1.581.63 0.97 5.5 5.5 0.5 VC 0.4 VC 0.4

TABLE 5 Firing conditions Blank Temperature Reduced Firing HIPTemperature Diameter Sample rise rate pressure temperature temperaturedifference Length (mm) (mm) No. (° C./min) (Pa) (° C.) (° C.) (° C.) LL₄ L₁ L₃ L₂ d_(A) d_(B) L/d_(A) II-1 5.0 80 1380 1370 10 8.8 0.0 4.5 0.14.2 1.38 1.34 6.4 II-2 4.5 100 1370 1360 10 8.9 0.0 2.4 0.2 6.3 1.371.33 6.5 II-3 6.0 150 1390 1375 15 8.9 0.1 5.9 — 2.9 1.38 1.32 6.4 II-45.0 80 1400 1390 10 8.6 0.0 4.4 — 4.2 1.42 1.92 6.1 II-5 5.0 100 13801370 10 8.9 0.0 8.9 1.33 1.33 6.7

TABLE 6 Blank Flank Number Co content wear of Sample (mass %) Co_(AC)/(mass %/mm) width processed No. Co_(AO) Co_(AC) Co_(BC) Co_(BC) S₄ S₁ S₃S₂ (μm) pieces II-1 1.5 1.8 5.0 0.36 — 0.6 6.0 0.02 120 1500 II-2 1.82.0 6.3 0.32 — 1.0 1.5 0.25 150 1600 II-3 0.0 0.0 4.0 0.00 0.1 0.5 —0.28 180 1000 II-4 2.3 2.6 4.8 0.54 — 0.5 — 0.02 160 1400 II-5 5.0 1.00— 300 600

As shown in Tables 4 to 6, sample Nos. II-1 to II-4 with Co_(AC) smallerthan Co_(BC) and with the gradient S₁ of the first portion larger thanthe gradient S₂ of the second portion had a small flank wear width, andsuccessfully processed a large number of pieces.

In particular, sample Nos. II-1 and II-2 with a third portion having agradient S₃ larger than the gradient S₁ between the second portion andthe first portion had a small flank wear width, and successfullyprocessed a large number of pieces. More specifically, sample No. II-1with the gradient S₃ being 2 to 50 percent by mass per milliliter had asmall flank wear width, and successfully processed a particularly largenumber of pieces.

EXAMPLE 3

The material powders used in Example 1 were also used to form compactsshown in Table 7. The compacts were fired under the conditions shown inTable 8. The blanks were used to form drills. The resultant drills weretested for drilling under the conditions described below. Tables 8 and 9show the results.

Drilling Test Conditions

Workpiece material: FP4 material, 0.06 mm thick, ten-layer stack

Drill shape: φ0.105 mm

Revolutions: 300 krpm

Feeding speed: 1.8 m/min

Evaluation items: the number of successfully bored pieces and the flankwear width (μm) of the tested drill

TABLE 7 First material powder Second material powder Co Co Compact sizeSample added Added added Added D_(A) D_(B) D_(A)/ H_(A) H_(B) H_(A)/ No.(mass %) Additive (mass %) (mass %) Additive (mass %) (mm) (mm) D_(B)(mm) (mm) (H_(A) + H_(B)) III-1 — Cr₃C₂ 0.4 10.0 Cr₃C₂ 1.0 2.35 2.400.98 5.5 5.5 0.5 VC 0.1 VC 0.4 III-2 — Cr₃C₂ 0.5 12.0 Cr₃C₂ 1.2 2.352.40 0.98 5.5 5.5 0.5 VC 0.2 VC 0.6 III-3 — Cr₃C₂ 0.4 20.0 Cr₃C₂ 2.12.35 2.40 0.98 5.5 5.5 0.5 VC 0.1 VC 0.8 III-4 12.0 Cr₃C₂ 0.5 12.0 Cr₃C₂1.5 2.35 2.40 0.98 5.5 5.5 0.5 VC 0.2 VC 0.7

TABLE 8 Firing conditions Blank Temperature Reduced Firing HIPTemperature Diameter Sample rise rate pressure temperature temperaturedifference Length (mm) (mm) No. (° C./min) (Pa) (° C.) (° C.) (° C.) LL₄ L₁ L₃ L₂ d_(A) d_(B) L/d_(A) III-1 5.0 80 1380 1370 10 9.0 0.0 4.50.3 4.2 2.00 1.91 4.5 III-2 5.0 80 1380 1370 10 9.0 0.0 4.5 0.3 4.2 1.981.90 4.5 III-3 5.0 80 1380 1370 10 9.0 0.0 4.5 0.3 4.2 1.96 1.89 4.6III-4 5.0 80 1380 1370 10 9.0 9.0 1.98 1.90 4.5

TABLE 9 Blank Flank Number Co content wear of Sample (mass %) Co_(AC)/(mass %/mm) width processed No. Co_(AO) Co_(AC) Co_(BC) Co_(BC) S₄ S₁ S₃S₂ (μm) pieces III-1 3.1 3.6 7.0 0.51 — 0.5 2.3 0.10 200 2500 III-2 3.94.2 9.0 0.47 — 0.5 8.3 0.05 150 3000 III-3 7.6 8.0 15.0 0.53 — 0.7 12.00.10 300 2000 III-4 12.0 — — 450 1000

As shown in Tables 7 to 9, sample Nos. III-1 to III-3 with Co_(AC)smaller than Co_(BC) and with the gradient S₁ of the first portionlarger than the gradient S₂ of the second portion had a small flank wearwidth, and successfully processed a large number of pieces.

EXAMPLE 4

As in Example 1, the first material powders and the second materialpowders shown in Table 10 were used for molding. For sample No. IV-5with d_(C)/d_(A) of the fired blank greater than 0.9, the lower punchwas fractured after 100 compacts were formed.

The compacts were heated at temperature rise rates shown in Table 10,and fired for 30 minutes at the temperatures shown in Table 10 as inExample 1. Then, the compacts underwent sinter-HIP firing at thetemperatures that are 30° C. lower than the temperatures in Table 10.The outer periphery of each resultant sintered body underwent centerlessgrinding to form a blank.

For the longitudinal direction of each resultant blank, the diametersd_(A), d_(B), d_(C) of part A, part B, and the protrusion, and changesin the Co content across the section from part A to the protrusion weremeasured through the EPMA analysis to detect the second to fourthportions, the gradients, and the lengths as in Example 1. The Co contentCo_(AO) was also measured. Further, both ends of the blank were observedwith a scanning electron microscope (SEM), and the mean particlediameter of the WC particles in part A and part B was calculated througha LUZEX analysis. Tables 11 and 12 show the results.

As in Example 1, the blanks were randomly placed into the joiningmachine. In the joining machine, the protrusion of each blank wasdetected, and the blanks were aligned to have their parts A and parts Bof the bodies arranged in the same directions to form a drill throughthe same processes as in Example 1. The protrusion allows part A andpart B to be easily distinguished. This allows easy formation of a drillwith a small content of Co in its portion adjacent to the cutting edges.For sample Nos. IV-1 to IV-5, and IV-7 to IV-13 with round protrusions,collisions between blanks being placed into the joining machine did notdamage the blanks.

The resultant drills were tested for drilling under the conditionsdescribed below. Table 12 shows the results.

Drilling Test Conditions

Workpiece material: BT material, one 10-layer stack, 2.5 mm thick

Drill shape: φ0.3 mm, undercutting

Revolutions: 100 krpm

Feeding speed: 1.5 m/min

Evaluation item: the number of successfully bored pieces

TABLE 10 First material powder Second material powder Firing conditionsSam- Co Co Compact shape Temperature Firing ple added Addi- Added addedAddi- Added D_(A) D_(B) D_(A)/ H_(A) H_(B) H_(A)/ rise rate temperatureNo. (mass %) tive (mass %) (mass %) tive (mass %) (mm) (mm) D_(B) (mm)(mm) (H_(A) + H_(B)) (° C./min) (° C.) IV-1 — Cr₃C₂ 0.4 8.0 Cr₃C₂ 0.61.58 1.63 0.97 5.5 5.5 0.5 10.0 1400 VC 0.1 VC 0.3 IV-2 — Cr₃C₂ 0.5 7.0Cr₃C₂ 0.5 1.50 1.65 0.91 4.5 6.5 0.4 7.0 1400 VC 0.2 VC 0.3 IV-3 — Cr₃C₂0.4 5.0 Cr₃C₂ 0.4 1.28 1.35 0.95 4.0 7.0 0.4 12.0 1370 VC 0.2 VC 0.3IV-4 2.0 VC 0.5 10.0 Cr₃C₂ 0.2 2.35 2.35 1.00 2.0 9.0 0.2 10.0 1420 VC0.4 IV-5 2.0 VC 0.5 10.0 Cr₃C₂ 0.2 2.35 2.35 1.00 2.0 9.0 0.2 10.0 1420VC 0.4 IV-6 — Cr₃C₂ 0.6 4.0 Cr₃C₂ 0.6 2.00 2.20 0.91 3.0 8.0 0.3 15.01390 IV-7 — Cr₃C₂ 0.4 8.0 Cr₃C₂ 0.6 1.58 1.63 0.97 5.5 5.5 0.5 7.0 1400VC 0.1 VC 0.3 IV-8 — — 13.0 Cr₃C₂ 0.6 1.58 1.63 0.97 6.5 4.5 0.6 15.01350 VC 0.3 IV-9 — Cr₃C₂ 0.4 8.0 Cr₃C₂ 0.6 1.10 1.20 0.92 4.0 7.0 0.45.0 1380 VC 0.3 VC 0.3 IV-10 — Cr₃C₂ 0.4 8.0 Cr₃C₂ 0.6 1.03 1.06 0.970.5 6.0 0.5 35.0 1400 VC 0.2 VC 0.3 IV-11 5.0 Cr₃C₂ 0.4 5.0 Cr₃C₂ 0.41.20 1.20 1.00 5.5 5.5 0.5 7.0 1420 VC 0.3 VC 0.3 IV-12 10.0  VC 0.510.0 Cr₃C₂ 0.3 1.00 1.00 1.00 5.5 5.5 0.5 7.0 1550 VC 0.2 IV-13 3.0Cr₃C₂ 0.4 7.0 Cr₃C₂ 0.6 1.03 1.06 0.97 7.0 4.0 0.6 10.0 1600 VC 0.2 VC0.3

TABLE 11 Blank Sample d_(A) d_(B) d_(C) d_(C)/ Length (mm) ProtrusionNo. (mm) (mm) (mm) d_(A) L L₄ L₁ L₃ L₂ L_(C) shape L/d_(A) IV-1 1.101.05 0.75 0.68 10.6 0.0 7.0 0.1 3.5 0.20 Round 9.6 IV-2 1.18 1.12 1.060.90 10.4 0.0 5.7 0.1 4.6 0.25 Round 8.8 IV-3 1.33 1.25 0.68 0.51 10.20.0 5.2 0.1 4.9 0.27 Round 7.7 IV-4 2.00 1.72 1.09 0.55 10.3 0.0 3.4 0.16.8 0.35 Round 5.2 IV-5 2.00 1.72 0.90 0.45 10.3 0.0 3.4 0.1 6.8 0.35Round 5.2 IV-6 1.58 1.58 1.53 0.97 10.8 0.0 5.1 0.1 5.6 0.30 Round 6.8IV-7 1.10 1.05 0.75 0.68 10.6 0.0 7.0 0.1 3.5 0.20 Sharp 9.6 IV-8 1.101.05 0.95 0.86 9.6 0.0 7.0 0.1 2.5 0.10 Round 8.7 IV-9 0.94 0.94 0.670.71 10.7 0.0 5.6 0.1 5.0 0.30 Round 11.4 IV-10 0.85 0.85 0.64 0.75 10.50.0 6.9 0.1 3.5 0.15 Round 12.4 IV-11 1.02 1.02 0.58 0.57 10.4 0.20Round 10.2 IV-12 0.86 0.86 0.58 0.67 9.8 0.20 Round 11.4 IV-13 0.81 0.810.56 0.69 10.4 0.20 Round 12.8

TABLE 12 Blank WC mean particle diameter Number of Sample Co content(mass %) Co_(AC)/ Co_(AO)/ Co_(CC)/ (mass %/mm) Part A Part B processedNo. Co_(AO) Co_(AC) Co_(BC) Co_(CC) Co_(BC) Co_(AC) Co_(AC) S₄ S₁ S₃ S₂(μm) (μm) pieces IV-1 1.3 1.5 6.5 0.5 0.19 0.83 0.33 — 0.53 10.0 0.0860.35 0.33 5000 IV-2 1.8 2.0 5.0 1.0 0.36 0.90 0.50 — 0.39 5.0 0.065 0.370.35 4600 IV-3 0.0 0.5 3.5 0.2 0.00 0.00 0.40 0.0 0.46 5.0 0.020 0.340.31 4800 IV-4 3.8 5.6 7.0 4.9 0.54 0.68 0.88 — 0.21 6.0 0.015 0.32 0.324000 IV-5 3.8 5.6 7.0 4.8 0.54 0.68 0.86 — 0.21 6.0 0.015 0.32 0.32 3900IV-6 0.1 0.16 1.8 0.11 0.06 0.69 0.69 — 0.16 4.0 0.071 0.31 0.31 4100IV-7 1.4 2.0 6.5 0.1 0.21 0.68 0.05 — 0.53 6.0 0.057 0.35 0.33 4300 IV-83.0 7.5 12.5 6.5 0.24 0.40 0.87 0.0 0.26 31.0 0.040 0.29 0.29 3200 IV-96.7 6.8 7.2 6.8 0.93 0.99 1.00 — 0.04 0.0 0.040 0.29 0.29 2400 IV-10 3.55.0 5.0 4.0 0.70 0.70 0.80 0.0 0.00 0.0 0.000 0.23 0.23 2300 IV-11 5.0 —0.32 0.29 2100 IV-12 10.0 — 0.32 0.28 2500 IV-13 5.5 — 0.33 0.27 2600

As shown in Tables 10 to 12, sample Nos. IV-1 to IV-8 with Co_(AC)smaller than Co_(BC) and with the gradient S₁ of the first portionlarger than the gradient S₂ of the second portion had a small flank wearwidth, and successfully processed a large number of pieces. The drillsof sample Nos. IV-10 to IV-13 with Co_(AC) equal to Co_(BC) and sampleNo. IV-9 with S₁ equal to S₂ successfully processed a small number ofpieces.

The drills of sample Nos. IV-1 to IV-8 also with Co_(CC) smaller thanCo_(AC) successfully processed a large number of pieces. Among sampleNos. IV-1 to IV-8, the drills of sample Nos. IV-1 to IV-3 successfullyprocessed a large number of pieces. Sample Nos. IV-1 to IV-3 had Co_(AC)ranging from 0.2 to 7 percent by mass, Co_(BC) ranging from 2 to 12percent by mass, the ratio Co_(AC)/Co_(BC) ranging from 0.1 to 0.6, andCo_(CC) ranging from 0.1 to 6 percent by mass, and the ratioCo_(CC)/Co_(AC) ranging from 0.1 to 0.8.

Unlike sample No. 5, for sample No. IV-5 with d_(C)/d_(A) of the firedblank smaller than 0.5, the entire protrusion was ground away whencutting edges are formed in the drill. The drill, which reduced the wearresistance of the cutting edges, processed a small number of pieces.

EXAMPLE 5

In contrast to the first material powder and the second material powderused for sample No. IV-1 in Example 4, the material powders with thesame characteristics as sample No. 1 in Example 1 were used, except thatthe WC powder had a mean particle diameter of 0.8 μm. In the same manneras for sample No. 1, elongated and cylindrical compacts were formed bycold isostatic pressing. In the compacts, D_(A)=D_(B)=6 mm, L=30 mm,D_(C)=3 mm, and L_(C)=3 mm. Also, H_(A)=10 mm, and H_(B)=20 mm. Thecompacts were fired at the same temperature rise rate and the samefiring temperature as for sample No. IV-1 to obtain sintered bodies, inwhich d_(A)=5.1 mm, d_(B)=4.8 mm, L_(A)=15 mm, L_(B)=9.3 mm,(L_(A)+L_(B))/d_(A)=4.8, Co_(AC)=2.7% by mass, Co_(BC)=7.1% by mass,Co_(CC)=2.5% by mass, the mean particle diameter of the WC particles inpart A was 0.85 μm, and the mean particle diameter of the WC particlesin part B was 0.80 μm. Cutting edges for a drill were successfullyformed in the resultant sintered bodies.

EXAMPLE 6

As in Example 4, the first material powders, the second materialpowders, and the third material powders shown in Table 13 were used toform blanks. For sample No. 5 with d_(C)/d_(A) of the fired blankgreater than 0.9, the lower punch was fractured after 100 compacts wereformed. For sample No. 6 with d_(C)/d_(A) smaller than 0.5, somecompacts had a portion near the protrusion of a compact damaged in themolding process, and the molding yields were low.

The compacts were heated at temperature rise rates shown in Table 14,and fired for 30 minutes at the temperatures shown in Table 14 as inExample 4. The compacts then underwent sinter-HIP firing at thetemperatures 30° C. lower than the temperatures in Table 14. The outerperiphery of each resultant sintered body underwent centerless grindingto form a blank.

To measure the length of each resultant blank, changes in the Co contentacross the section from part A to the protrusion were measured throughthe EPMA analysis to detect the second to fourth portions, thegradients, and the lengths as in Example 4. The Co content Co_(AO) wasalso measured. Further, both ends of the blank were observed with theSEM, and the mean particle diameter of the WC particles in part A andpart B was calculated through a LUZEX analysis. Tables 14 and 15 showthe results.

As in Example 4, the blanks were randomly placed into the joiningmachine. In the joining machine, the protrusion of each blank wasdetected, and the blanks were aligned to have their parts A and parts Bof the bodies arranged in the same directions to form an end millthrough the same processes as in Example 4. The protrusion allows part Aand part B to be easily distinguished. This allows easy formation of anend mill with a small content of Co in its portion adjacent to thecutting edges. Tables 14 and 15 show the results.

For sample Nos. VI-1 to VI-3, and VI-5 to VI-12 with round protrusions,the blanks were not damaged when colliding one another in the process ofbeing placed into the joining machine.

The resultant end mills were tested for machining under the conditionsdescribed below. Table 15 shows the results.

End Mill Machining Test Conditions

Workpiece material: S45C block material

End mill shape: φ1 mm, two-flute

Revolutions: 25 krpm

Feeding speed: 220 mm/min

Cut (depth ap): 1.5 mm

Cut (width ae): 0.05 mm

Evaluation item: the distance machined by side cutting

TABLE 13 First material powder Second material powder Third materialpowder Compact size Sam- Co Added Co Added Co Added H_(A)/ ple added(mass added (mass added (mass D_(A) D_(B) D_(A)/ H_(A) H_(B) (H_(A) +No. (mass %) Additive %) (mass %) Additive %) (mass %) Additive %) (mm)(mm) D_(B) (mm) (mm) H_(B)) VI-1 10.0 Cr₃C₂ 0.6 — Cr₃C₂ 0.4 8.0 Cr₃C₂0.6 1.58 1.63 0.97 5.5 5.5 0.5 VC 0.3 VC 0.1 VC 0.3 VI-2 8.0 Cr₃C₂ 0.4 —Cr₃C₂ 0.4 5.0 Cr₃C₂ 0.4 1.28 1.35 0.95 4.0 7.0 0.4 VC 0.3 VC 0.2 VC 0.3VI-3 7.0 Cr₃C₂ 0.5 — Cr₃C₂ 0.5 7.0 Cr₃C₂ 0.5 1.50 1.65 0.91 4.5 6.5 0.4VC 0.3 VC 0.2 VC 0.3 VI-4 15.0 Cr₃C₂ 0.6 — Cr₃C₂ 0.4 15.0 Cr₃C₂ 0.6 1.581.63 0.97 5.5 5.5 0.5 VC 0.3 VC 0.1 VC 0.3 VI-5 5.0 Cr₃C₂ 0.6 — Cr₃C₂0.6 4.0 Cr₃C₂ 0.6 2.00 2.20 0.91 3.0 8.0 0.3 VI-6 6.0 Cr₃C₂ 0.2 2.0 VC0.5 10.0 Cr₃C₂ 0.2 2.35 2.35 1.00 2.0 9.0 0.2 VC 0.4 VC 0.4 VI-7 18.0Cr₃C₂ 0.6 — 13.0 Cr₃C₂ 0.6 1.58 1.63 0.97 6.5 4.5 0.6 VC 0.3 VC 0.3 VI-88.0 Cr₃C₂ 0.6 — Cr₃C₂ 0.4 8.0 Cr₃C₂ 0.6 1.10 1.20 0.92 4.0 7.0 0.4 VC0.3 VC 0.3 VC 0.3 VI-9 2.0 Cr₃C₂ 0.6 2.0 Cr₃C₂ 0.4 8.0 Cr₃C₂ 0.6 1.031.06 0.97 5.0 6.0 0.5 VC 0.3 VC 0.2 VC 0.3 VI-10 5.0 Cr₃C₂ 0.6 5.0 Cr₃C₂0.4 5.0 Cr₃C₂ 0.4 1.20 1.20 1.00 5.5 5.5 0.5 VC 0.3 VC 0.3 VC 0.3 VI-11— Cr₃C₂ 0.6 10.0  VC 0.5 10.0 Cr₃C₂ 0.3 1.00 1.00 1.00 5.5 5.5 0.5 VC0.3 VC 0.2 VI-12 — Cr₃C₂ 0.6 3.0 Cr₃C₂ 0.4 7.0 Cr₃C₂ 0.6 1.03 1.06 0.977.0 4.0 0.6 VC 0.3 VC 0.2 VC 0.3

TABLE 14 Firing conditions Temperature Firing Blank Sample rise ratetemperature d_(A) d_(B) d_(C) d_(C)/ Protrusion Length (mm) No. (°C./min) (° C.) (mm) (mm) (mm) d_(A) shape L L₄ L₁ L₃ L₂ L_(C) L/d_(A)VI-1 10.0 1400 1.10 1.05 0.75 0.68 Round 10.6 0.0 7.0 0.1 3.5 0.20 9.6VI-2 12.0 1370 1.33 1.25 0.68 0.51 Round 10.2 0.0 5.2 0.1 4.9 0.27 7.7VI-3 7.0 1400 1.18 1.12 1.06 0.90 Round 10.4 0.0 5.7 0.1 4.6 0.25 8.8VI-4 7.0 1370 1.10 1.04 0.75 0.68 Sharp 10.6 0.0 7.0 0.1 3.5 0.20 9.6VI-5 15.0 1390 1.58 1.58 1.53 0.97 Round 10.8 0.0 5.1 0.1 5.6 0.30 6.8VI-6 10.0 1420 2.00 1.72 0.90 0.45 Round 10.3 0.0 3.4 0.1 6.8 0.35 5.2VI-7 15.0 1350 1.10 1.05 0.95 0.86 Round 9.6 0.0 7.0 0.1 2.5 0.10 8.7VI-8 5.0 1380 0.94 0.94 0.67 0.71 Round 10.7 0.0 5.6 0.1 5.0 0.30 11.4VI-9 35.0 1400 0.85 0.85 0.64 0.75 Round 10.5 0.0 6.9 0.1 3.5 0.15 12.4VI-10 7.0 1420 1.02 1.02 0.58 0.57 Round 10.4 0.20 10.2 VI-11 7.0 15500.86 0.86 0.58 0.67 Round 9.8 0.20 11.4 VI-12 10.0 1600 0.81 0.81 0.560.69 Round 10.4 0.20 12.8

TABLE 15 Blank WC mean particle diameter Machining Sample Co content(mass %) Co_(AC)/ Co_(CC)/ Co_(AO)/ (mass %/mm) Part A Part B distanceNo. Co_(AO) Co_(AC) Co_(BC) Co_(CC) Co_(BC) Co_(AC) Co_(AC) S₄ S₁ S₃ S₂(μm) (μm) (m) VI-1 1.5 2.6 5.0 0.6 0.52 2.54 0.58 — 0.27 4.0 0.029 0.350.33 50 VI-2 0.5 2.1 3.5 5.5 0.60 2.62 0.24 — 0.19 3.0 0.020 0.34 0.3149 VI-3 2.5 3.0 5.0 3.6 0.60 1.20 0.83 0.0 0.21 7.0 0.022 0.37 0.35 47VI-4 6.3 7.0 12.0 13.9 0.58 1.99 0.90 — 0.49 13.0 0.086 0.35 0.33 44VI-5 0.05 0.1 3.1 0.7 0.03 7.00 0.50 — 0.49 2.0 0.054 0.31 0.31 42 VI-65.1 5.4 7.0 5.8 0.77 1.07 0.94 — 0.38 2.0 0.015 0.32 0.32 40 VI-7 7.58.6 12.2 14.1 0.70 1.64 0.87 0.0 0.23 17.0 0.120 0.29 0.29 33 VI-8 6.8 —— 0.00 0.0 0.000 0.29 0.29 23 VI-9 3.3 3.3 6.2 3.3 0.53 0.88 1.00 0.00.30 6.0 0.057 0.23 0.23 22 VI-10 5.0 1.00 1.00 1.00 — 0.32 0.29 21VI-11 9.6 10.0 9.5 0.96 0.99 1.04 — 0.32 0.28 24 VI-12 5.5 5.5 5.4 1.009.98 1.00 — 0.33 0.27 25

As shown in Tables 13 to 15, sample Nos. VI-1 to VI-7 with Co_(AC)smaller than Co_(BC) and with the gradient S₁ of the first portionlarger than the gradient S₂ of the second portion had a small flank wearwidth and an elongated machining distance. For sample No. VI-12 withCo_(AC) equal to Co_(BC), sample No. VI-9 with Co_(CC) equal to Co_(AC),sample No. VI-11 with Co_(CC) smaller than Co_(AC), and sample Nos. VI-8and VI-10 with Co_(AC) equal to Co_(BC) and Co_(CC) equal to Co_(AC),the end mills achieved short machining distances. In contrast, forsample Nos. VI-1 to VI-7 with Co_(AC) smaller than Co_(BC) and withCo_(CC) larger than Co_(AC), the end mills achieved long machiningdistances.

Among sample Nos. VI-1 to VI-7, for sample Nos. VI-1 to VI-4 withCo_(AC) ranging from 0.2 to 7 percent by mass, Co_(BC) from 3 to 12percent by mass, the ratio Co_(AC)/Co_(BC) ranging from 0.1 to 0.6,Co_(CC) ranging from 3 to 14 percent by mass, and the ratioCo_(CC)/Co_(AC) ranging from 1.2 to 3, the drills achieved longmachining distances.

In sample Nos. VI-1 to VI-4, the Co content in a central area of thefirst end face was higher than the Co content in the outer periphery ofthe first end face. The Co content Co_(AO) was 0.1 to 6.5 percent bymass, and the ratio Co_(AO)/Co_(AC) was 0.1 to 0.9.

EXAMPLE 7

In contrast to the first material powders, the second material powders,and the third material powders used for sample Nos. VI-6 and VI-10 inExample 6, material powders with the same formulated composition assample Nos. VI-6 and VI-10 in Example 1 were used, except that the WCpowder had a mean particle diameter of 0.8 μm. In the same manner as forsample Nos. VI-6 and VI-10, elongated and cylindrical compacts wereformed by cold isostatic pressing. In the compacts, D_(A)=D_(B)=6 mm,L=30 mm, D_(C)=3 mm, and L_(C)=3 mm. Also, H_(A)=10 mm, and H_(B)=20 mm.The compacts were fired at the same temperature rise rate and the samefiring temperature as for sample No. VI-1 to obtain the sintered bodiesof sample Nos. VII-13 and VII-14.

For sample No. VII-13, d_(A)=5.1 mm, d_(B)=4.8 mm, L_(A)=15 mm,L_(B)=9.3 mm, (L_(A)+L_(B))/d_(A)=4.8, Co_(AC)=5.6% by mass,Co_(AO)=5.0% by mass, Co_(BC)=7.2% by mass, Co_(CC)=6.2% by mass, the WCparticles in part A had a mean particle diameter of 0.85 μm, and the WCparticles in part B had a mean particle diameter of 0.80 μm.

For sample No. VII-14, d_(A)=5.0 mm, d_(B)=5.0 mm, L=25.0 mm,Co_(AC)=Co_(AO)=Co_(BC)=Co_(CC)=5.0% by mass, the WC particles in part Ahad a mean particle diameter of 0.80 μm, and the WC particles in part Bhad a mean particle diameter of 0.80 μm.

Cutting edges were formed in the resultant sintered bodies to form 4MFKend mills (KYOCERA Corporation). The resultant end mills had two shapeshaving different cutting edge lengths. The end mills were used forcutting under the conditions: workpiece material: SUS304, processingdiameter: φ8 mm, cutting type: shouldering, processing speed: 85 m/min,revolutions: 3300 rpm, feed: 0.035 mm/flute, depth of cut: 5 mm, widthof cut: 3 mm, and wet cutting. Sample No. VII-13 had a length of cut of40 m, and the cutting edges of the end mills had normal wear. Incontrast, sample No. VII-14 had a length of cut of 24 m, and fractureswere observed near the end mill rotation axis.

REFERENCE SIGNS LIST

1 drill (cutting tool)

2 blank (cutting tool blank)

part A first end

part B second end

3 shank

5 cutting edge

6 flute

7 neck

8 body

11 first portion

12 second portion

13 third portion

14 fourth portion

15 protrusion

d_(A) first end diameter

d_(B) second end diameter

d_(C) diameter at contact with first end A of protrusion

D_(A) diameter of portion adjacent to lower punch

D_(B) diameter of portion adjacent to upper punch

D_(C) diameter at contact between raw protrusion of compact and lowerpart of compact

1. A rod, comprising: a cemented carbide member containing tungstencarbide (WC) and cobalt (Co), the cemented carbide member having anelongated shape, and the cemented carbide member comprising: a first endportion in a longitudinal direction, the first end portion having a Cocontent Co_(AC); a second end portion in the longitudinal direction, thesecond end portion having a Co content Co_(BC), the Co content Co_(AC)being smaller than the Co content Co_(BC); a first portion on a side ofthe first end portion, the first portion having a gradient S₁representing a change in a Co content per milliliter; and a secondportion on a side of the second end portion, the second portion having agradient S₂ representing a change in a Co content per milliliter, thegradient S₁ being greater than the gradient S₂.
 2. The rod according toclaim 1, wherein the Co content Co_(AC) is 0.2 to 7 percent by mass, andthe Co content Co_(BC) is 2 to 12 percent by mass.
 3. The rod accordingto claim 1, wherein a ratio Co_(AC)/Co_(BC) of the Co content Co_(AC) tothe Co content Co_(BC) is 0.2 to 0.7.
 4. The rod according to claim 1,wherein the first end portion comprises a central area and an outerperiphery in a direction perpendicular to the longitudinal direction,and the central area has a Co content higher than a Co content in theouter periphery.
 5. The rod according to claim 4, wherein when the outerperiphery has a Co content Co_(AO) of 0.1 to 6.5 percent by mass, aratio Co_(AO)/Co_(AC) of the Co content Co_(AO) to the Co contentCo_(AC) is 0.1 to 0.9.
 6. The rod according to claim 1, wherein thegradient S₁ is 0.2 to 1.0 percent by mass per milliliter, and thegradient S₂ is 0 to 0.2 percent by mass per milliliter.
 7. The rodaccording to claim 1, wherein the cemented carbide member furthercomprises a third portion disposed between the first portion and thesecond portion, the third portion having a gradient S₃, the gradient S₃being larger than the gradient S₁ of the first portion.
 8. The rodaccording to claim 7, wherein the gradient S₃ is 2 to 50 percent by massper milliliter.
 9. The rod according o claim 1, wherein the firstportion has a longitudinal length L₁ and the second portion has alongitudinal length L₂, and a ratio L₁/L₂ is 0.2 to
 2. 10. The rodaccording to claim 1, wherein a diameter d_(A) of the first end portionis 2 millimeters (mm) or less, a diameter d_(B) of the second endportion is 2 mm or less, and a ratio L/d_(A) of a longitudinal length Lof the cemented carbide member to the diameter d_(A) is 3 or more. 11.The rod according to claim 10, wherein a ratio d_(A)/d_(B) of thediameter d_(A) to the diameter d_(B) is 1.02 to 1.20.
 12. The rodaccording to claim 1, further comprising: a protrusion located on afirst end face of the first end portion.
 13. The rod according to claim12, wherein the protrusion has a Co content smaller than the Co contentCo_(AC) in the first end portion.
 14. The rod according to claim 13,wherein a Co content Co_(CC) in a tip of the protrusion is 0.1 to 6percent by mass, and a ratio Co_(CC)/Co_(AC) of the Co content Co_(CC)to a Co content Co_(AC) in a central area of the first end portion in adirection perpendicular to the longitudinal direction is 0.1 to 0.8. 15.The rod according to claim 13, wherein the Co content in the protrusionis higher than the Co content Co_(AC) in the first end portion.
 16. Therod according to claim 15, wherein a Co content Co_(CC) in a tip of theprotrusion is 3 to 14 percent by mass, and a ratio Co_(CC)/Co_(AC) ofthe Co content Co_(CC) to the Co content Co_(AC) in a central area ofthe first end portion in a direction perpendicular to the longitudinaldirection is 1.2 to
 3. 17. The rod according to claim 12, wherein thefirst end portion has a diameter d_(A), the protrusion has a diameterd_(C) at a position of contact with the first end portion, and a ratiod_(C)/d_(A) of the diameter d_(C) to the diameter d_(A) is 0.5 to 0.9.18. A cutting tool, comprising: a cemented carbide member containingtungsten carbide (WC) and cobalt (Co), the cemented carbide memberhaving an elongated shape, and the cemented carbide member comprising: afirst end portion in a longitudinal direction, the first end portionhaving a Co content Co_(AC); a second end portion in the longitudinaldirection, the second end portion having a Co content Co_(BC), the Cocontent Co_(AC) being smaller than the Co content Co_(BC); cutting edgesat least on a side of the first end portion; a shank portion on a sideof the second end portion; a first portion on a side of the first endportion, the first portion having a gradient S₁ representing a change ina Co content per milliliter; and a second portion on a side of thesecond end portion, the second portion having a gradient S₂ representinga change in a Co content per milliliter, the gradient S₁ being greaterthan the gradient S₂.
 19. A method for manufacturing a cutting tool, themethod comprising: placing the rod according to claim 1 randomly into ajoining machine; distinguishing the first end portion of the rod fromthe second end portion in the joining machine and arranging the rod in apredetermined direction; placing the second end portion of the rod incontact with a shank and joining the second end portion to the shank;and forming cutting edges in a portion of the rod including the firstend portion.
 20. A method for manufacturing a cutting tool, the methodcomprising: placing the rod according to claim 14 randomly into ajoining machine; arranging the rod in a predetermined direction in thejoining machine based on whether the protrusion is detected or theprotrusion is not detected; joining the second end portion of the rod toa shank; and forming cutting edges in a portion of the rod including thefirst end portion.